The holes are all in line so you should be able to mount it parallel or perpendicular. I haven’t tried since I did the t-slot stuff but if it can hold the Atlantik, this should be easy enough.Do you have any idea if these arm mounts can be installed on the light in a 'long' orientation rather than 'wide'? I have a peninsula, so I would love to use an arm mount and install the light in an orientation where it's going to be covering more of the tank. I had the same issue with the Kessil AP9X, which was the main reason I didn't get that light.